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CAVIAR – Radiometric Calibration Meeting

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					                   CAVIAR – Radiometric Calibration Meeting

                         10:30 - 14:30, 17th November, 2006

                                Lecture Theatre, B95
                            National Physical Laboratory

Attendees :
      Stuart Newman ( stu.newman@metoffice.gov.uk )
      Paul Green ( p.green@imperial.ac.uk )
      Juliet Pickering (j.pickering@imperial.ac.uk )
      Tom Gardiner ( tom.gardiner@npl.co.uk )
      Marc Coleman ( marc.coleman@npl.co.uk )
      Melanie Williams ( melanie.Williams@npl.co.uk )
      Eric Usadi ( eric.usadi@npl.co.uk )
      Martin Dury ( martin.dury@npl.co.uk )
      Theo Theocharous ( theo.theocharous@npl.co.uk )

Agenda

   1. Introduction and overview of NPL facilities (Tom Gardiner, Theo
      Theocharous)
   2. Summary of instrumentation (Paul Green – TAFTS, Stuart Newman –ARIES)
   3. Proposed design of calibration blackbody (Eric Usadi)
   4. Discussion of design and interface issues (All)
   5. Wrap-up, including agreed actions and timescales (All)

Summary

A series of short presentations were given which summarised NPL capabilities,
reviewed the instrumentation, and described the initial design plans for the calibration
blackbody (CBB). Copies of these talks will be distributed to the group.

A number of important design issues were identified during the talks and the
following discussion :
     The low temperature range was more important than the high temperature
       range. The CBB will not need to be operated above room temperature.
     In order to calibrate TAFTS the CBB must be able to interface with both the
       nadir and zenith viewports. ARIES will only require interfacing to the nadir
       view.
     A second reference scene will be required for the TAFTS calibration. Options
       include a cold (liquid nitrogen) target or the existing TAFTS external BB.
     The option for calibrating the TAFTS external BB against the NPL AMBER
       facility needs to be considered.
     The instrumental apertures and fields of view need to be confirmed for the
       position in which the CBB will be located.
     The CBB will require a physical coupling to TAFTS and a free-space coupling
       to ARIES. The gas purging arrangements for both set-ups needs to be
       considered.
      It was confirmed that the calibration campaigns would take place at NPL, and
       the CBB design would therefore not need to be a ruggedised field system.

Other relevant issues that were raised included :
    Instrument lineshape (ILS) – The ARIES team has started to look at their
       ILS function, and this is something that NPL has experience of. The LINEFIT
       software may be of particular use for this.
    Zero reading – an area that will require further consideration is how to verify
       the zero levels for both the TAFTS and ARIES instruments.
    Detector linearity – Theo has done a lot of work on detector (particularly
       MCT) linearity, and dealing with this will be one of the calibration issues.
    Uncertainity budget – it was agreed that a common approach to assessing the
       overall uncertainty of the FT measurements would be important in ensuring
       the consistency and comparability of the different instruments.
    Timetable for primary calibration phase – the primary calibration needs to
       take place close enough to the first field campaign (~July 2008) to ensure that
       the calibration is valid for the campaign, while giving enough time to analyse
       and possibly react to the results. March 2008 was suggested as being suitable
       for this.
    Next Meeting – It was agreed that a follow-up technical meeting should be
       arranged in February or March 2007.

Actions
    Confirmation of apertures and field of views to be sent to NPL (Stuart, Paul)
    Distribute details of instrument lineshape software tool (Tom)
    Determine revised temperature range for CBB(Eric)
    Arrange next technical meeting (Tom).

				
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